A respiratory burst oxidase homolog protein in Pyrus regulates stigmatic ROS production to control pollen tube growth

Accumulation of reactive oxygen species (ROS) in the stigma is crucial for the sexual reproduction of flowering plants. However, the derivation of stigmatic production of ROS in pear is still largely unknown. Here, we identified a respiratory burst oxidase homolog (Rboh) protein in pear (Pyrus bretschneideri), PbRbohD1, which is required for ROS accumulation in the stigma. Knockdown of PbRbohD1 by the antisense oligodeoxynucleotide (as-ODN) technique resulted in significant reductions of stigma ROS levels. Interaction analysis indicated that the N-terminal region of PbRbohD1 interacted with the stigmatic Rho of plant (ROP) protein PbrROP2, and PbRbohD1 colocalized with PbrROP2 in the plasma membrane. PbrROP2 activated the PbRbohD1 protein, thereby stimulating the production of ROS. Knockdown of PbrROP2 in the stigma drastically reduced the ROS levels. Thus, during pear stigma development, PbrROP2 and PbRbohD1 work together to control the stigmatic ROS level. Reducing the stigmatic ROS level with a ROS scavenger, sodium salicylate (Na-SA), accelerated the growth of self-pollen tubes in the style and increased the fruit set rate. Our results uncover a signaling pathway that regulates the levels of stigmatic ROS, providing the physiological basis for improving pollination efficiency and fruit set rate.